The potential of free-space optical communication systems is well established as a means of providing high bandwidth data links between two points on a line of sight basis. Such systems are being considered for a number of applications, including as elements of communication links in metropolitan areas and for local area networks in open plan offices.
Co-pending patent application U.S. patent application Ser. No. 10/483,738 (A. M. Scott et al.) discloses a dynamic optical reflector and interrogation system employing a combination of spacing-controllable etalon and a retro-reflector arranged to reflect light received via the etalon back through the etalon towards the light source.